Uptake and metabolism of the explosive RDX by the marine seaweeds Portieria hornemannii and Acrosiphonia coalita, and uptake of the explosive TNT by algal extracts of Portieria hornemannii

Abstract:

This study examines the interactions between explosive environmental contaminants and marine seaweeds. The scope of this thesis includes studies done on the explosive RDX with tissue cultures of marine seaweeds, as well as studies on the explosive TNT with seaweed extracts.
The ability of two different marine species of macroalgae to take up and metabolize the nitroheterocyclic explosive RDX was examined. RDX uptake was analyzed using axenic microplantlet suspension culture systems of the red tropical seaweed Portieria hornemannii and the green temperate seaweed Acrosiphonia coalita. Algal tissue cultures were challenged with seawater containing an RDX concentration of 9.0 mg/L for an exposure time of 170 hours. The photosynthetic viability of the two different marine seaweeds was monitored using chlorophyll a fluorescence techniques. The photosynthetic viability study subjected suspension cultures of algal biomass to RDX concentrations of 9.0 and 18 mg/L for a duration of 40 minutes.
Algal suspensions of the marine seaweeds Portieria and Acrosiphonia did not take up or metabolize the nitroheterocyclic explosive RDX. Furthermore RDX was not shown
to have any effect on the photosynthetic viability of chlorophyll a fluorescence. The photosynthetic fluorescence parameter Fv/Fm did not change over short time periods of exposure to RDX. None of the associated chlorophyll a fluorescence parameters changed upon exposure to RDX concentrations of 9.0 mg/L and 18 mg/L. In conclustion these studies suggest that RDX cannot be bioremediated by macroalgae. Furthermore, RDX poses no toxic threat to photosynthesis of macroalgae.
The ability of crude and soluble extracts of the red tropical marine seaweed Portieria hornemannii to biotransform the aromatic explosive TNT into reductive metabolites was investigated. Crude extracts are defined as ground and homogenized algal tissue in phosphate buffer. Soluble extracts are defined as the decanted supernatant of crude extracts that have been centrifuged at 15,000 g for 10 minutes. The coenzymes NADPH and NADH were added as reducing agents to both the soluble and crude extracts. Crude and water soluble extracts of Portieria were shown to take up the aromatic explosive TNT. However no reductive biotransformation products of TNT, 2-ADNT and 4-ADNT were found in the liquid phase.
A simple model for TNT binding to amine-rich proteins in the algal biomass constituents was developed to account for removal of TNT from the liquid phase by both soluble and crude extracts of Portieria. TNT binding in crude extracts accounted for 92 % of the TNT in the liquid phase, whereas 34% of the TNT could be accounted for in crude extracts containing the coenzyme NADPH. The binding model accounted for all the TNT removal in soluble extracts. The addition of the coenzymes NADPH and NADH was shown to have no effect on TNT reduction by soluble extracts. In conclusion, these studies suggest that Portieria extracts are not capable of metabolizing TNT. However algal detritus does have a finite capacity for TNT uptake.